Perhaps I missed it on my annual reads through the instructions, but I cannot recall seeing a statement: "This is the definitive path to figuring your tax." For the personal income tax instructions, that pathway is clear for almost everyone.
Take your business income items, and add those up.
Take your business expense items, and add those up.
Subtract expense from income. Done...
Personal income tax is much more complicated than small business income tax. Large corporations and partnerships are more complicated than small businesses, but those types of businesses want the additional complexity.